As an outgrowth of the Investigator's description of the technique of angiographically demonstrating sites of gastrointestinal bleeding many questions have arisen regarding the present techniques. The investigators are requesting renewal of their present grant so as to further refine present and develop newer approaches to this difficult and important problem. During the next twelve months, the investigators will attempt to improve radiographic and catheterization techniques of the examination by the use of magnification angiography. In addition, they will evaluate nonthrombogenic catheter materials and attempt to consistently develop methods of superselective catheterization and also evaluate a simple radiographic method of assessing blood flow in the mesenteric circulation. Another specific aim during the next grant period will be to try to answer the question of how long infusions are necessary to satisfactorily control arterial and venous bleeding. We will also attempt to determine the effect on the liver of hepatic arterial infusion of vasopressin. Various mechanical means of controlling gastrointestinal hemorrhage will also be evaluated which will include intraarterial radiofrequency coagulation, balloon catheters, and injectible silastic catheters.